[hchen19@beeblebrox parser]$ python
Python 1.5.2 (#1, Jul  5 2001, 03:02:19)  [GCC 2.96 20000731 (Red Hat Linux 7.1 2 on linux-i386
Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam
>>> from tree import *
>>> root=PlusNode(NumNode(2), TimesNode(NumNode(3), PlusNode(NumNode(3), NumNode(5))))
>>> root.interpret({})
26.0
>>> root=PlusNode(NumNode(2), TimesNode(NumNode(3), MinusNode(NumNode(3), NumNode(5))))
>>> root.interpret({})
-4.0
>>>